U.S. Pat. No. 2,772,561 discloses an apparatus for calibrating an indicating flowmeter in a pipeline. The apparatus includes plug means insertable in the pipeline to form a movable seal within the pipeline, the plug means being adapted to be propelled through the pipeline by the flowing fluid at the velocity thereof. the apparatus includes first and second signal means mounted in longitudinally spaced relationship at predetermined points in the pipeline, the signal means being adapted to be actuated by the arrival of the plug means thereat. The apparatus includes electrical circuit means connecting the first and second signal means with the flowmeter, whereby the indicating flowmeter is energized by the arrival of the plug means at the first signal means and de-energized by the arrival of the plug means at the second signal means.
U.S. Pat. No. 3,021,703 discloses an apparatus for calibrating a meter such as a positive displacement meter in a pipe line, the apparatus comprising a calibration barrel adapted to be fluidly connected into the pipe line. A pulse generator is operatively connected to the meter and on flow of fluid through the meter, pulses are generated. Electronic switching means are electrically connected to the pulse generator and an electronic counter means is electrically connected to the electric switching means. Adjacent each end of the barrel and operatively connected thereto are flow indicating means which are adapted to be actuated by flow of fluid from the pipe line through the calibration barrel whereby pulses from the pulse generator are led into the electronic counter means by sequential actuation of the flow indicating means by flow of fluid from the pipe line through the calibration barrel.
U.S. Pat. No. 3,273,375 discloses a calibrating barrel comprising an outer tubular housing closed at each end, a reduced diameter and length inner tubular barrel supported within the housing providing an annulus between the exterior of the barrel and the interior of the housing, and a wall partitioning the annulus into two longitudinal portions. The housing has fluid ports therein communicating with each annulus portion wherein fluid flowing into one port flows within one annulus portion through the barrel, through the other annulus portion and out of the other port. A free piston is disposed in the barrel and first and second spaced apart detector switches are actuated by the passage of the piston as it moves in the barrel.